The present invention is generally related to mesh nodes in optical networks and, in particular, to mesh node systems with add/drop capabilities.
Current optical networks are mostly DWDM (Dense Wavelength Division Multiplexing) networks in which particular wavelengths of light define communication channels so that multiple communication channels can be carried on a single optical fiber. An ITU (International Telecommunications Union) standard specifies the particular channel wavelengths and the spacing between these channels. DWDM is based upon WDM (Wavelength Division Multiplexing), an earlier ITU standard in which a smaller number of wavelength channels are carried by an optical fiber with the channels further spaced apart. It should be noted that the term DWDM, as used herein, refers to the more inclusive sense of wavelength definition of communication channels so as to include the ITU WDM and DWDM standards, unless specifically stated otherwise.
Whether in an optical network or not, a mesh node is located at the intersection of at least three, typically four or more, network links. Hence the name, “mesh.” The network links provide alternate network directions for communication signals leaving the node. A system operating at a mesh node directs the communication signals entering the node from one network direction to another direction as instructed. For example, the destination address of a signal wavelength instructs a node on the direction of these signals are to be sent.
A mesh node can also provide a location for signals to be dropped from the network or added to the network. The “drop” signals are typically intended for a client located near the node. The “add” signals are typically originated from clients near the node for transport by the network. The facility to add and drop signals is a particular problem for optical networks due to the particular nature of light.
Current DWDM mesh node systems have add and drop functions on the bi-directional links connected to a mesh node. In particular, the add function is located on the link leading away from the node and the drop function on the link leading to the node. Thus a problem arises for the add signals if the link is broken or the node on the other side of the link is defective or inoperative. There is no alternate link to reroute the add signals.
Hence there is a need for flexible mesh node systems in which add and drop signals can be rerouted. The signals are not limited to particular directions, and hence are considered “directionless.”
It should be noted that in the drawings above, elements having like features or functions in different drawings often have the same reference numerals to better aid an understanding of the present invention and its embodiments.